Message-Id: <564ba9d6b8f88d139be556d039aadb4b8e078eba.1641398395.git.fweimer@redhat.com>
Date:   Wed, 05 Jan 2022 17:03:36 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     "Andy Lutomirski" <luto@...nel.org>
Cc:     linux-arch@...r.kernel.org,
        "Linux API" <linux-api@...r.kernel.org>,
        linux-x86_64@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        linux-mm@...ck.org, "the arch/x86 maintainers" <x86@...nel.org>,
        musl@...ts.openwall.com, <libc-alpha@...rceware.org>,
        <linux-kernel@...r.kernel.org>,
        "Dave Hansen" <dave.hansen@...el.com>,
        "Kees Cook" <keescook@...omium.org>,
        Andrei Vagin <avagin@...il.com>
Subject: [PATCH v3 3/3] x86: Add test for arch_prctl(ARCH_VSYSCALL_CONTROL)

Signed-off-by: Florian Weimer <fweimer@...hat.com>
---
v3: Patch split out.

 tools/arch/x86/include/uapi/asm/prctl.h       |   2 +
 tools/testing/selftests/x86/Makefile          |   7 +-
 .../testing/selftests/x86/vsyscall_control.c  | 891 ++++++++++++++++++
 3 files changed, 899 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/x86/vsyscall_control.c

diff --git a/tools/arch/x86/include/uapi/asm/prctl.h b/tools/arch/x86/include/uapi/asm/prctl.h
index 754a07856817..aad0bcfbf49f 100644
--- a/tools/arch/x86/include/uapi/asm/prctl.h
+++ b/tools/arch/x86/include/uapi/asm/prctl.h
@@ -18,4 +18,6 @@
 #define ARCH_MAP_VDSO_32	0x2002
 #define ARCH_MAP_VDSO_64	0x2003
 
+#define ARCH_VSYSCALL_CONTROL	0x5001
+
 #endif /* _ASM_X86_PRCTL_H */
diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index 0993d12f2c38..4c751836bfeb 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -18,7 +18,7 @@ TARGETS_C_32BIT_ONLY := entry_from_vm86 test_syscall_vdso unwind_vdso \
 			test_FCMOV test_FCOMI test_FISTTP \
 			vdso_restorer
 TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
-			corrupt_xstate_header amx
+			corrupt_xstate_header amx vsyscall_control
 # Some selftests require 32bit support enabled also on 64bit systems
 TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall
 
@@ -107,3 +107,8 @@ $(OUTPUT)/test_syscall_vdso_32: thunks_32.S
 # state.
 $(OUTPUT)/check_initial_reg_state_32: CFLAGS += -Wl,-ereal_start -static
 $(OUTPUT)/check_initial_reg_state_64: CFLAGS += -Wl,-ereal_start -static
+
+# This test does not link against anything (neither libc nor libgcc).
+$(OUTPUT)/vsyscall_control_64: \
+	LIBS := -Wl,-no-pie -static -nostdlib -nostartfiles
+	CFLAGS += -fno-pie -fno-stack-protector -fno-builtin -ffreestanding
diff --git a/tools/testing/selftests/x86/vsyscall_control.c b/tools/testing/selftests/x86/vsyscall_control.c
new file mode 100644
index 000000000000..ee966f936c89
--- /dev/null
+++ b/tools/testing/selftests/x86/vsyscall_control.c
@@ -0,0 +1,891 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * vsyscall_lockout.c - check that disabling vsyscall works
+ * Copyright (C) 2021 Red Hat, Inc.
+ *
+ * This test requires vsyscall=xonly or vsyscall=emulate.  With
+ * vsyscall=emulate, ARCH_VSYSCALL_CONTROL cannot turn off vsyscall
+ * completely (reads still work), but this is not tested here.
+ */
+
+#include <stddef.h>
+
+#include <asm/prctl.h>
+#include <asm/vsyscall.h>
+#include <linux/errno.h>
+#include <linux/fcntl.h>
+#include <linux/signal.h>
+#include <linux/time.h>
+#include <linux/types.h>
+#include <linux/unistd.h>
+
+#ifndef ARCH_VSYSCALL_CONTROL
+#define ARCH_VSYSCALL_CONTROL	0x5001
+#elif ARCH_VSYSCALL_CONTROL != 0x5001
+#error wrong vlaue for ARCH_VSYSCALL_CONTROL
+#endif
+
+
+static inline long syscall0(int nr)
+{
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall1(int nr, long arg0)
+{
+	register long rdi asm("rdi") = arg0;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall2(int nr, long arg0, long arg1)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi), "r" (rsi)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall3(int nr, long arg0, long arg1, long arg2)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	register long rdx asm("rdx") = arg2;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi), "r" (rsi), "r" (rdx)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall4(int nr, long arg0, long arg1, long arg2, long arg3)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	register long rdx asm("rdx") = arg2;
+	register long r10 asm("r10") = arg3;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi), "r" (rsi), "r" (rdx),
+			    "r" (r10)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall5(int nr, long arg0, long arg1, long arg2, long arg3,
+			    long arg4)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	register long rdx asm("rdx") = arg2;
+	register long r10 asm("r10") = arg3;
+	register long r8 asm("r8") = arg4;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi), "r" (rsi), "r" (rdx),
+			    "r" (r10), "r" (r8)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long vsyscall2(long addr, long arg0, long arg1)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	unsigned long result;
+
+	__asm__ volatile ("callq *%%rax"
+			  : "=a" (result)
+			  : "0" (addr), "r" (rdi), "r" (rsi)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static void __attribute__ ((noreturn)) sys_exit(int status)
+{
+	syscall1(__NR_exit, status);
+	__builtin_unreachable();
+}
+
+static int sys_access(const char *pathname, int mode)
+{
+	return syscall2(__NR_access, (long) pathname, mode);
+}
+
+static int sys_mkdir(const char *pathname, __kernel_mode_t mode)
+{
+	return syscall2(__NR_mkdir, (long) pathname, mode);
+}
+
+static int sys_open(const char *pathname, int flags, __kernel_mode_t mode)
+{
+	return syscall3(__NR_open, (long) pathname, flags, mode);
+}
+
+static long sys_read(int fd, void *buffer, size_t length)
+{
+	return syscall3(__NR_read, fd, (long) buffer, length);
+}
+
+static long sys_write(int fd, const void *buffer, size_t length)
+{
+	return syscall3(__NR_write, fd, (long) buffer, length);
+}
+
+static int sys_mount(const char *source, const char *pathname,
+		     const char *fstype, unsigned long flags,
+		     const void *data)
+{
+	return syscall5(__NR_mount, (long) source, (long) pathname,
+			(long) fstype, flags, (long) data);
+}
+
+static void sigabrt(void)
+{
+	syscall2(__NR_kill, syscall0(__NR_getpid), SIGABRT);
+}
+
+/*
+ * String buffers.
+ */
+
+struct buffer {
+	char *position;
+	char *limit;
+};
+
+static void buffer_init(struct buffer *b, char *start, size_t length)
+{
+	b->position = start;
+	b->limit = start + length;
+}
+
+static void buffer_append(struct buffer *b, char ch)
+{
+	if (b->position >= b->limit)
+		sigabrt();
+	*b->position = ch;
+	++b->position;
+}
+
+static void buffer_append_string(struct buffer *b, const char *p)
+{
+	while (*p) {
+		buffer_append(b, *p);
+		++p;
+	}
+}
+
+static void buffer_append_dec_1(struct buffer *b, unsigned long val)
+{
+	if (val != 0) {
+		buffer_append_dec_1(b, val / 10);
+		buffer_append(b, '0' + (val % 10));
+	}
+}
+
+static void buffer_append_dec(struct buffer *b, unsigned long val)
+{
+	if (val == 0) {
+		buffer_append(b, '0');
+		return;
+	}
+	buffer_append_dec_1(b, val);
+}
+
+/*
+ * Output to standard output.
+ */
+
+static void print_char(char byte)
+{
+	if (sys_write(1, &byte, 1) < 0)
+		sigabrt();
+}
+
+static void print_string(const char *p)
+{
+	while (*p) {
+		print_char(*p);
+		++p;
+	}
+}
+
+static void print_dec_1(unsigned long val)
+{
+	if (val != 0) {
+		print_dec_1(val / 10);
+		print_char('0' + (val % 10));
+	}
+}
+
+static void print_dec(unsigned long val)
+{
+	if (val == 0)
+		print_char('0');
+	else
+		print_dec_1(val);
+}
+
+static void print_signed_dec(long val)
+{
+	if (val < 0) {
+		print_char('-');
+		print_dec(-(unsigned long)val);
+	} else
+		print_dec(val);
+}
+
+static void print_message(unsigned int lineno, const char *tag, const char *p)
+{
+	print_string(__FILE__);
+	print_char(':');
+	print_dec(lineno);
+	print_char(':');
+	print_char(' ');
+	print_string(tag);
+	print_char(':');
+	print_char(' ');
+	print_string(p);
+}
+
+static void print_info(unsigned int lineno, const char *p)
+{
+	print_message(lineno, "info", p);
+}
+
+static void print_error(unsigned int lineno, const char *p)
+{
+	print_message(lineno, "ERROR", p);
+}
+
+static void print_failure(int lineno, const char *label, long ret)
+{
+	print_error(lineno, label);
+	print_string(" failed: ");
+	print_signed_dec(ret);
+	print_char('\n');
+}
+
+static void print_time(int lineno, const char *label, struct timeval tv)
+{
+	print_info(lineno, label);
+	print_string(": ");
+	print_dec(tv.tv_sec);
+	print_char(' ');
+	print_dec(tv.tv_usec);
+	print_char('\n');
+}
+
+/*
+ * Process-failing (v)syscall wrappers.
+ */
+
+static void xgettimeofday(struct timeval *tv)
+{
+	long ret = syscall2(__NR_gettimeofday, (long) tv, 0);
+
+	if (ret != 0) {
+		print_failure(__LINE__, "gettimeofday", ret);
+		sigabrt();
+	}
+}
+
+static void xvgettimeofday(struct timeval *tv)
+{
+	long ret = vsyscall2(VSYSCALL_ADDR, (long) tv, 0);
+
+	if (ret) {
+		print_failure(__LINE__, "vgettimeofday", ret);
+		sigabrt();
+	}
+}
+
+static int sys_arch_prctl(int code, unsigned long addr)
+{
+	return syscall2(__NR_arch_prctl, code, addr);
+}
+
+static void xclose(int fd)
+{
+	long ret = syscall1(__NR_close, fd);
+
+	if (ret < 0) {
+		print_failure(__LINE__, "close", ret);
+		sigabrt();
+	}
+}
+
+static void xwrite_byte(int fd, char b)
+{
+	long ret = sys_write(fd, &b, 1);
+
+	if (ret != 1) {
+		print_failure(__LINE__, "write", ret);
+		sigabrt();
+	}
+}
+
+static int xread_byte(int fd)
+{
+	char b;
+	long ret = sys_read(fd, &b, 1);
+
+	if (ret != 1) {
+		print_failure(__LINE__, "read", ret);
+		sigabrt();
+	}
+	return b;
+}
+
+static void xpipe(int fds[static 2])
+{
+	long ret = syscall2(__NR_pipe2, (long) fds, O_CLOEXEC);
+
+	if (ret != 0) {
+		print_failure(__LINE__, "pipe2", ret);
+		sigabrt();
+	}
+}
+
+static __kernel_pid_t xfork(void)
+{
+	long ret = syscall0(__NR_fork);
+
+	if (ret < 0) {
+		print_failure(__LINE__, "fork", ret);
+		sigabrt();
+	}
+	return ret;
+}
+
+static void xexecve(const char *pathname, char **argv, char **envp)
+{
+	long ret;
+
+	ret = syscall3(__NR_execve, (long) pathname, (long) argv, (long) envp);
+	print_failure(__LINE__, "execve", ret);
+	sigabrt();
+}
+
+static __kernel_pid_t xwaitpid(__kernel_pid_t pid, int *status, int options)
+{
+	long ret = syscall4(__NR_wait4, pid, (long) status, options, 0);
+
+	if (ret < 0) {
+		print_failure(__LINE__, "wait4", ret);
+		sigabrt();
+	}
+	return ret;
+}
+
+/*
+ * Various helpers.
+ */
+
+static void vsyscall_disable(void)
+{
+	long ret = sys_arch_prctl(ARCH_VSYSCALL_CONTROL, 0);
+
+	if (ret != 0)
+		print_failure(__LINE__, "arch_prctl(ARCH_VSYSCALL_CONTROL, 0)", ret);
+}
+
+static void vsyscall_enable(void)
+{
+	long ret = sys_arch_prctl(ARCH_VSYSCALL_CONTROL, 1);
+
+	if (ret != 0)
+		print_failure(__LINE__, "arch_prctl(ARCH_VSYSCALL_CONTROL, 1)", ret);
+}
+
+static long difftime(struct timeval first, struct timeval second)
+{
+	return second.tv_usec - first.tv_usec +
+		(second.tv_sec - first.tv_sec) * 1000 * 1000;
+}
+
+static void ensure_proc_is_mounted(int *status)
+{
+	int ret;
+
+	if (sys_access("/proc/version", 0) == 0)
+		return;
+
+	ret = sys_mkdir("/proc", 0555);
+	if (ret == EEXIST)
+		return;
+	if (ret != 0) {
+		print_failure(__LINE__, "could not create /proc", ret);
+		*status = 1;
+		return;
+	}
+	ret = sys_mount("none", "/proc", "proc", 0, NULL);
+	if (ret != 0) {
+		print_failure(__LINE__, "could not mount /proc", ret);
+		*status = 1;
+		return;
+	}
+	if (sys_access("/proc/version", 0) != 0) {
+		print_error(__LINE__, "no /proc/version after mounting /proc");
+		*status = 1;
+		return;
+	}
+}
+
+/*
+ * Individual subtest functions.
+ */
+
+static void check_time(int *status)
+{
+	struct timeval initial_time = { -1, -1 };
+	struct timeval vsyscall_time = { -1, -1 };
+	struct timeval final_time = { -1, -1 };
+	long vsyscall_diff, final_diff;
+
+	xgettimeofday(&initial_time);
+	xvgettimeofday(&vsyscall_time);
+	xgettimeofday(&final_time);
+	vsyscall_diff = difftime(initial_time, vsyscall_time);
+	final_diff = difftime(vsyscall_time, final_time);
+
+	print_time(__LINE__, "initial gettimeofday", initial_time);
+	print_time(__LINE__, "vsyscall gettimeofday", vsyscall_time);
+	print_time(__LINE__, "final gettimeofday", final_time);
+
+	if (initial_time.tv_sec < 0 || initial_time.tv_usec < 0 ||
+	    vsyscall_time.tv_sec < 0 || vsyscall_time.tv_usec < 0 ||
+	    final_time.tv_sec < 0 || final_time.tv_usec < 0) {
+		print_error(__LINE__, "negative time\n");
+		*status = 1;
+	}
+
+	print_info(__LINE__, "differences: ");
+	print_signed_dec(vsyscall_diff);
+	print_char(' ');
+	print_signed_dec(final_diff);
+	print_char('\n');
+
+	if (vsyscall_diff < 0 || final_diff < 0) {
+		/*
+		 * This may produce false positives if there is an active NTP.
+		 */
+		print_error(__LINE__, "time went backwards\n");
+		*status = 1;
+	}
+}
+
+static void check_lockout_after_fork(int *status, int twice)
+{
+	__kernel_pid_t pid;
+	struct timeval vsyscall_time;
+	int wstatus;
+
+	if (twice) {
+		__kernel_pid_t pid_outer;
+
+		print_info(__LINE__, "checking that lockout is inherited by fork\n");
+
+		pid_outer = xfork();
+		if (pid_outer == 0) {
+			vsyscall_disable();
+			/*
+			 * Logic for the subprocess follows below.
+			 */
+		} else {
+			xwaitpid(pid_outer, &wstatus, 0);
+			if (wstatus != 0) {
+				print_error(__LINE__, "unexpected exit status: ");
+				print_signed_dec(wstatus);
+				print_char('\n');
+				*status = 1;
+			}
+			return;
+		}
+	} else
+		print_info(__LINE__, "checking that lockout works after one fork\n");
+
+	pid = xfork();
+	if (pid == 0) {
+		if (!twice)
+			vsyscall_disable();
+		/*
+		 * This should trigger a fault.
+		 */
+		xvgettimeofday(&vsyscall_time);
+		sys_exit(0);
+	}
+	xwaitpid(pid, &wstatus, 0);
+	switch (wstatus) {
+	case 0:
+		print_error(__LINE__, "no crash after lockout\n");
+		*status = 1;
+		break;
+	case 0x0100:
+		*status = 1;
+		break;
+	case SIGSEGV:
+		print_info(__LINE__, "termination after lockout\n");
+		break;
+	default:
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+
+	if (twice)
+		sys_exit(*status);
+
+	/*
+	 * Status in the parent process should be unaffected.
+	 */
+	xvgettimeofday(&vsyscall_time);
+}
+
+static void check_no_lockout_after_enable(int *status)
+{
+	__kernel_pid_t pid;
+	struct timeval vsyscall_time;
+	int wstatus;
+
+	print_info(__LINE__, "checking that vsyscall can be re-enabled\n");
+
+	pid = xfork();
+	if (pid == 0) {
+		vsyscall_disable();
+		vsyscall_enable();
+		xvgettimeofday(&vsyscall_time);
+		print_time(__LINE__, "vsyscall time after re-enable", vsyscall_time);
+		sys_exit(0);
+	}
+
+	xwaitpid(pid, &wstatus, 0);
+	if (wstatus != 0) {
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+static void check_no_lockout_after_execve(char **argv, int *status)
+{
+	__kernel_pid_t pid;
+	int wstatus;
+
+	print_info(__LINE__, "checking that lockout is not inherited by execve\n");
+	pid = xfork();
+	if (pid == 0) {
+		struct timeval vsyscall_time;
+		char *new_argv[3];
+
+		xvgettimeofday(&vsyscall_time);
+		vsyscall_disable();
+
+		/*
+		 * Re-exec the second stage.  See main_2 below.
+		 */
+		new_argv[0] = argv[0];
+		new_argv[1] = "2";
+		new_argv[2] = NULL;
+		xexecve(argv[0], new_argv, new_argv + 2);
+	}
+
+	xwaitpid(pid, &wstatus, 0);
+	if (wstatus != 0) {
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+static int has_vsyscall_map(int pid, int *status)
+{
+	int result = 0;
+	char maps_path[50];
+	int fd;
+
+	/*
+	 * Construct /proc/PID/maps path.
+	 */
+	{
+		struct buffer b;
+
+		buffer_init(&b, maps_path, sizeof(maps_path));
+		buffer_append_string(&b, "/proc/");
+		if (pid == 0)
+			buffer_append_string(&b, "self");
+		else
+			buffer_append_dec(&b, pid);
+		buffer_append_string(&b, "/maps");
+		buffer_append(&b, 0);
+	}
+
+	fd = sys_open(maps_path, O_RDONLY, 0);
+	if (fd < 0) {
+		print_error(__LINE__, "maps file ");
+		print_string(maps_path);
+		print_string(": ");
+		print_signed_dec(fd);
+		print_char('\n');
+		*status = 1;
+	}
+
+	/*
+	 * Search for "[vsyscall]\n".
+	 */
+	{
+		char buf[4096];
+		long ret;
+
+		for (size_t i = 0; i < sizeof(buf); ++i)
+			buf[i] = 0;
+		ret = sys_read(fd, buf, sizeof(buf));
+
+		if (ret < 0 || ret >= sizeof(buf))
+			print_failure(__LINE__, "read", ret);
+		else {
+			char *bracket = buf;
+
+			while (1) {
+				while (*bracket && *bracket != '[')
+					++bracket;
+				if (*bracket != '[')
+					/*
+					 * End of file has been reached.
+					 */
+					break;
+				++bracket;
+				if (bracket[0] == 'v'
+				    && bracket[1] == 's'
+				    && bracket[2] == 'y'
+				    && bracket[3] == 's'
+				    && bracket[4] == 'c'
+				    && bracket[5] == 'a'
+				    && bracket[6] == 'l'
+				    && bracket[7] == 'l'
+				    && bracket[8] == ']'
+				    && bracket[9] == '\n') {
+					result = 1;
+					break;
+				}
+			}
+		}
+	}
+
+	xclose(fd);
+	return result;
+}
+
+static void check_vsyscall_in_self_maps(int *status)
+{
+	__kernel_pid_t pid;
+	int wstatus;
+
+	print_info(__LINE__, "checking [vsyscall] in /proc/self/maps\n");
+
+	pid = xfork();
+	if (pid == 0) {
+		if (!has_vsyscall_map(0, status)) {
+			print_error(__LINE__, "[vsyscall] missing\n");
+			*status = 1;
+		}
+		vsyscall_disable();
+		if (has_vsyscall_map(0, status)) {
+			print_error(__LINE__, "[vsyscall] present after disable\n");
+			*status = 1;
+		}
+		vsyscall_enable();
+		if (!has_vsyscall_map(0, status)) {
+			print_error(__LINE__, "[vsyscall] missing after enable\n");
+			*status = 1;
+		}
+		sys_exit(*status);
+	}
+
+	xwaitpid(pid, &wstatus, 0);
+	if (wstatus != 0) {
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+static void check_vsyscall_maps_for_subprocess(int *status)
+{
+	__kernel_pid_t pid;
+	int wstatus;
+	int outer_to_inner[2];
+	int inner_to_outer[2];
+
+	/*
+	 * Create pipes used to synchronize the two processes.
+	 */
+	xpipe(outer_to_inner);
+	xpipe(inner_to_outer);
+
+	print_info(__LINE__, "checking [vsyscall] in /proc/PID/maps\n");
+
+	pid = xfork();
+	if (pid == 0) {
+		xclose(outer_to_inner[1]);
+		xclose(inner_to_outer[0]);
+
+		xread_byte(outer_to_inner[0]);
+		vsyscall_disable();
+		xwrite_byte(inner_to_outer[1], 101);
+
+		xread_byte(outer_to_inner[0]);
+		vsyscall_disable();
+		xwrite_byte(inner_to_outer[1], 102);
+
+		sys_exit(0);
+	}
+
+	xclose(outer_to_inner[0]);
+	xclose(inner_to_outer[1]);
+
+	if (!has_vsyscall_map(pid, status)) {
+		print_error(__LINE__, "subprocess starts without [vsyscall]");
+		*status = 1;
+	}
+
+	xwrite_byte(outer_to_inner[1], 1);
+	xread_byte(inner_to_outer[0]);
+
+	if (has_vsyscall_map(pid, status)) {
+		print_error(__LINE__, "subprocess has [vsyscall] after disable");
+		*status = 1;
+	}
+
+	xwrite_byte(outer_to_inner[1], 2);
+	xread_byte(inner_to_outer[0]);
+
+	if (has_vsyscall_map(pid, status)) {
+		print_error(__LINE__, "subprocess lacks [vsyscall] after enable");
+		*status = 1;
+	}
+
+	xclose(outer_to_inner[1]);
+	xclose(inner_to_outer[0]);
+
+	xwaitpid(pid, &wstatus, 0);
+	if (wstatus != 0) {
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+static void check_einval(int *status)
+{
+	long ret;
+
+	ret = sys_arch_prctl(ARCH_VSYSCALL_CONTROL, 2);
+	if (ret != -EINVAL) {
+		print_error(__LINE__, "arch_prctl(ARCH_VSYSCALL_CONTROL, 2) returned ");
+		print_signed_dec(ret);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+/*
+ * Second stage: Check that the lockout is not inherited across execve.
+ * Used from check_no_lockout_after_execve.
+ */
+static int main_2(void)
+{
+	struct timeval vsyscall_time = { -1, -1 };
+	int status = 0;
+
+	xvgettimeofday(&vsyscall_time);
+	print_time(__LINE__, "vsyscall gettimeofday after fork", vsyscall_time);
+	if (vsyscall_time.tv_sec < 0 || vsyscall_time.tv_usec < 0)
+		status = 1;
+
+	return status;
+}
+
+static int main(int argc, char **argv)
+{
+	int status = 0;
+
+	if (argc > 1) {
+		switch (*argv[1]) {
+		case '2':
+			return main_2();
+		default:
+			print_string("usage: ");
+			print_string(argv[0]);
+			print_string("\n");
+			return 1;
+		}
+	}
+
+	ensure_proc_is_mounted(&status);
+
+	if (has_vsyscall_map(0, &status))
+		print_info(__LINE__, "vsyscall active at process start\n");
+	else
+		print_error(__LINE__, "vsyscall inactive at process start\n");
+
+
+	check_time(&status);
+	check_lockout_after_fork(&status, 0);
+	check_lockout_after_fork(&status, 1);
+	check_no_lockout_after_enable(&status);
+	check_no_lockout_after_execve(argv, &status);
+	check_vsyscall_in_self_maps(&status);
+	check_vsyscall_maps_for_subprocess(&status);
+	check_einval(&status);
+
+	print_info(__LINE__, "testing done, exit status: ");
+	print_signed_dec(status);
+	print_char('\n');
+	return status;
+}
+
+static void __attribute__ ((used)) main_trampoline(long *rsp)
+{
+	sys_exit(main(*rsp, (char **) (rsp + 1)));
+}
+
+__asm__(".text\n\t"
+	".globl _start\n"
+	"_start:\n\t"
+	".cfi_startproc\n\t"
+	".cfi_undefined rip\n\t"
+	"movq %rsp, %rdi\n\t"
+	"callq main_trampoline\n\t" /* Results in psABI %rsp alignment.  */
+	".cfi_endproc\n\t"
+	".type _start, @function\n\t"
+	".size _start, . - _start\n\t"
+	".previous");
-- 
2.33.1

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